Di-, tri- and tetra(hydroxy phenyl)alkanes have previously been reacted with compounds such as epichlorohydrin to form the glycidyl ethers thereof. These ethers have been cured to produce resins which were expected to possess good high-temperature properties, said properties being in large demand.
The feasibility of producing epoxides from such poly(hydroxy phenyl)alkanes is recognized in the art due to the availability of starting materials such as leucaurin.
Tris(4-hydroxyphenyl)methane, commonly known as leucaurin, has been prepared by the reduction of aurin with zinc dust and acetic acid. It (and isomers or homologs of it) may also be prepared by the condensation of a phenol with the appropriate hydroxy substituted aromatic ketone or aldehyde. For instance, tris(4-hydroxyphenyl)ethane is prepared by the reaction of phenol and 4-hydroxyacetophenone (see U.S. Pat. No. 3,579,542). One can prepare derivatives having substituents on the phenol-derived phenyl rings from the correspondingly substituted phenol reactant.
Derivatives having alkoxy substituents on the ketone- or aldehyde-derived phenyl ring may be prepared according to U.S. Pat. No. 3,787,451.
Dearborn et al. (I.E.C. 45, No. 12) reported the preparation of epoxides from polyfunctional phenols by a process wherein the phenol, epichlorohydrin ("epi") and caustic were mixed and heated, thereby coupling and dehydrohalogenating in a single operation. I have determined that the leucaurin epoxide prepared according to their method had an epoxy functionality of about 2 and (when cured) a relatively poor high-temperature performance (see Table 7 in Example 8 herein). Also see U.S. Pat. Nos. 2,857,362 and 2,863,852 (Dearborn et al.), which pertain to the above-reported research.
U.S. Pat. No. 2,965,611 (Schwarzer) teaches the epoxidation of tri- and tetra(hydroxyphenyl)alkanes wherein no more than two epoxyalkoxyphenyl groups are attached to the same carbon. Schwarzer's epoxidation method was similar to Dearborn's, except that the phenol-epi mixture was heated to reflux prior to the addition of aqueous caustic. However, he prepared an epoxide only from a tetrakis-compound.
British Pat. No. 875,811 (Neumann) discloses the use of solid, rather than aqueous, caustic in preparing the Schwarzer tris-epoxide by an otherwise similar method.
The advantages of epoxy resins for a wide variety of applications are well known but it has been necessary to use otherwise generally less tractable types of resins--most notably polyimides--for applications in which a Heat Distortion Temperature (HDT) in excess of about 315.degree. C. is specified. To the best of the present inventor's knowledge, the highest HDT's reported for known epoxy resins are 257.degree. C. (for the tetraglycidyl ether of 1,2,2,3-tetrakis(4-hydroxyphenol)propane, U.S. Pat. No. 2,965,611); 303.degree. C. (for the triglycidyl ether of 1,2,2-tris(4-hydroxyphenyl)propane, British Pat. No. 875,811) and 315.degree. C. (for "Epoxylite high temperature resins" manufactured by the Epoxylite Corporation and believed to be based on 1,1,2,2,-tetrakis(4-glycidyloxyphenyl)ethane). Of course, properties other than HDT, such as pot life, thermal stability, flexural strength, resistance to heat and moisture, resistance to chemicals and/or solvents and processability are also highly important. It is a balanced combination of high HDT and good performance in other regards that is essential to the commercial success of any resin. This combination has not really been realized and the teachings of the prior art fail to make obvious which, if any, possible resin structures can provide it.